1. Field of the Invention
The present invention relates to an image pickup apparatus having a camera shake correction function.
2. Description of the Related Art
As an image pickup apparatus, as well known, there are a digital camera, a monitoring camera, and the like. The image pickup apparatus is generally provided with an automatic focusing mechanism and an automatic exposure control mechanism. Recently, the image pickup apparatus is further provided with a camera shake correction mechanism so as to suppress image quality degradation of a captured image occurring due to camera shake. The camera shake occurs when the image pickup apparatus rotates or shifts in accordance with movement of hands or arms holding the image pickup apparatus. The camera shake is a low-frequency vibration on the order of 1 to 10 Hz. Accordingly, for the purpose of correcting the camera shake, the low-frequency vibration of the image pickup apparatus is detected, and then an imaging device or a correction lens contained in an image pickup lens is caused to move so as to cancel the low-frequency vibration. Thereby, occurrence of image blur on a screen is suppressed.
The image blur due to the rotation of the image pickup apparatus (hereinafter referred to as angle camera shake) occurs when a release button is depressed or the like. On the other hand, the image blur due to parallel shifting of the image pickup apparatus (hereinafter referred to as shift camera shake) occurs when arms holding a camera move, for example. In macro image capturing at high magnification or the like, the shift camera shake affects the captured image adversely more than the angle camera shake. The angle camera shake can be detected by an angular velocity sensor. However, it is difficult for the angular velocity sensor to accurately detect the shift camera shake. In view of the above, recently, in addition to the angular velocity sensor, an acceleration sensor is provided to the image pickup apparatus, so as to detect an acceleration of the image pickup apparatus due to the parallel shifting thereof and suppress occurrence of the shift camera shake based on the detected acceleration (see Japanese Patent Laid-Open Publication No. 2010-286721 and US Patent Application Publication No. 2011/0063458 corresponding to Japanese Patent Laid-Open Publication No. 2010-025961).
In the image pickup apparatus disclosed in each of Japanese Patent Laid-Open Publication No. 2010-286721 and US Patent Application Publication No. 2011/0063458, it is possible to correct both the angle camera shake and the shift camera shake. However, it is only when mechanical movable sections in the image pickup apparatus do not operate that the angle camera shake and the shift camera shake can be corrected with precision. It is because, while the movable sections operate, vibration of the image pickup apparatus in accordance with an internal acceleration thereof due to the movable sections results in noise in the angular velocity sensor and the acceleration sensor. In a lens unit, the mechanical movable sections are a magnification lens, a focusing lens, an aperture stop, and the like. In the image pickup apparatus disclosed in each of Japanese Patent Laid-Open Publication No. 2010-286721 and US Patent Application Publication No. 2011/0063458, while the lens unit operates, the camera shake correction mechanism is suspended, and after the operation of the lens unit is stopped, the operation of the camera shake correction mechanism is resumed.
In most cases, while performing zooming operation, focusing, exposure control, or the like, a user observes a through-image on a monitor screen or looks through an optical viewfinder, so as to determine the framing of an image to be captured. As the camera shake correction mechanism is suspended while the lens unit operates, the image quality of the through-image or the image looked through the viewfinder degrades due to the camera shake, and thereby it becomes harder to determine the framing of the image to be captured. In the macro image capturing, in particular, since the magnification is high, degradation of the image quality is prominent even when slight camera shake occurs. Further, in moving-image capturing, the zooming operation or the like is performed in conjunction with the image capturing. Thus, there is a problem in that the image quality of the moving image degrades since the camera shake correction mechanism is suspended every time the zooming operation or the like is performed.